Attenuating sound control system for electronic musical instruments



Sept. 14, 1965 SHIGEAKI MABUCHI ATTENUATING SOUND CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Dec. 9.

d; jib ewg United States Patent Japan Filed Dec. 9, 1960, Ser. No. 74,968 Claims priority, application Japan, May 7, 1960, 35/23:,073 1 Claim. (Cl. 84-113) This invention relates to an attenuating sound control system for electronic musical instruments.

Among various systems for producing so-called attenuating sound effects in electronic musical instruments which effects are analogous to those obtained by string instruments played with plectrums, fingers or by percussion instruments are included a system wherein a time constant circuit comprising a condenser C and a resistor R is combined with a switching circuit of an electronic tube or a semiconductor, a system wherein the oscillator output is controlled by varying exponentially the voltage impressed upon an oscillator according to charge and discharge of a condenser C, a system using a mechanical vibration and the like.

It is the principal object of this invention to provide a novel attenuating sound control system which is different from any of said prior control systems.

Another object of this invention is to provide a purely electrical control system which is equivalent to above mentioned system utilizing a mechanical vibration.

An essential feature of this invention consists in that it is not only possible to produce attenuating sound effects from a single unit, but also can effect frequency division.

Second feature of this invention consists in that the interrupter of the signal is a switching circuit free of any mechanical contacts.

Third feature of this invention consists in that it comprises a mere combination of L, C and R and does not utilize any active element.

Fourth feature of this invention consists in that control of attenuation, i.e., lengthening or shortening of signals corresponding to a plurality of keyboards can be simul taneously effected by a single contact.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, as to its organization together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIGURE 1 shows a connection diagram of one embodiment of this invention explaining the principle thereof;

FIGURE 2 is a connection diagram of a circuit actually applied for controlling the attenuation time of a musical instrument.

Referring now to FIGURE 1, there is provided a pair of magnetic cores 1a and 1b. The core 1a is provided with primary and secondary windings 2a and 3a wound thereon and the core 1]) is provided with primary and secondary windings 2b and 3b wound thereon, said primary windings and secondary windings being connected in series, respectively. The primary windings are biased by a direct current source 4 through a suitable choke coil 5 while a resonance condenser 6 is connected between the output terminals b and [2' across the secondary windings. Input terminals a and a are connected across the primary windings via a coupling condenser 7 which also serves as one element of the primary resonance circuit.

The circuit described above is substantially the same as that of the so-called parametron elements excepting 3,206,535 Patented Sept. 14, 1965 that the circuit shown in FIGURE 1 is provided with resistors 8, 9 and 10 for controlling attenuation time, switches 11 and 12 for controlling the attenuation time and a switch 13 for controlling the signal on the secondary side. Thus, if these resistors 8, 9 and 10 were omitted or short circuited, the circuit would have the same circuit construction as the parametron elements. Accordingly, supposing that the secondary circuit will resonate at a frequency of about f/ 2 when a signal of frequency f arrives at the input terminals a and a, then an oscillating voltage of a frequency of f/ 2 would appear across the output terminals. Now, if this short circuited portion is replaced by resistors as shown in FIGURE 1 and the magnitude of these resistors were increased gradually, the oscillation of f/2 would be ceased when the resistance reaches a certain magnitude. If it is assumed that the inductance contributing to the oscillation in the secondary circuit by L, the condenser by C, the resistance inserted by R, direct current resistance of the secondary windings by r, modulation index of the inductance by I, detuning factor by 6 and the term due to non-linearity of the magnetic core by [31 (where I represents an oscillation current having a frequency of f/Z), the condition of oscillation will be represented by the following formula oscillation will be stopped when the resistance R is increased beyond a magnitude represented by,

f P s+BIa/Z 2) Actually, I will decrease gradually so that it may be assumed that the oscillation will be stopped when the resistance is increased beyond R man/1 4 7 It is to be noted that even when the inserted resistance is varied rapidly, decrease of this current I is relatively slow when compared with the rate of change of resistance value if the value of the varied resistance is near R represented by the Equation 3.

Thus, signals having attenuating oscillation can be easily obtained by utilizing this phenomena. More particularly, the resistance of the resistor 10 is selected to be slightly larger (represented by (R a-12 than R the resistance of the resistor 8 be nearly equal (represented by R to R and the resistance of resistor 9 is also selected to be nearly equal (represented by R;,) to R On the other hand, sum (R +R of the resistance of the resistors 8 and 9 are selected to be a little smaller than R In this case, attenuation of oscillating signals will begin when the switch 13 is opened after it has once been closed to initiate oscillation while the switch 11 is in the closed position. Since resistance which is quickly thrown into this circuit is equal to R +R -R period of attenuation is long. But in case where the switch 12 alone is closed, when the switch 13 is opened after it has been closed, the resistance which acts to damp oscillation would be equal to (R +R +R whereby attenuating signals having shorter attenuating time than in the previous case can be produced. Where both of the switches 11 and 12 are open, the resistance after the switch 13 is opened will be equal to R +R +R +R -2R and in this case, if this signal is heard by ear as an acoustic output, a fast attenuating signal which is similar to that produced when the signal channel is directly interrupted can be obtained.

If one tries to switch in or off the output signal by closing and opening the excitation signals having an attenuation time of a length comparable with those obtainable by this system, in other words, signals in which it takes 1 to 3 seconds for their maximum 1 amplitude to decrease by about 30 db, it is necessary to make very large the Q of the oscillating circuit which is almost impossible under conditions for use in electronic musical instruments. By using resistance change of the nature above described, it is easy to produce quick attenuation that is to make the time required for attenuating about 30 db from the maximum amplitude to about 10 to 30 microseconds.

Since the circuit shown in FIG. 1 operates similarly as the so-called parametron elements so far as the trans mission of the signal is concerned, it can eifect /2 frequency division and theoretically, by proper selection of the secondary circuit it can effect frequency conversion at any integer ratio. Thus, for instance, in an electronic musical instrument comprising twelve master oscillators constituting one octave, if the instant system is utilized as a means for producing a signal of the frequency of another octave .by converting the output of the respective master oscillators, not only frequency conversion but also switching of the signal can be effected by the same circuit without the necessity of directly interrupting the signal circuit by keyboard contacts.

In the embodiment shown in FIGURE 1, it'is required to use switches for controlling attenuation time of the number proportional to the number of keys of the keyboards, for instance, but thesse switches may be made common to the respective keyboards. FIGURE 2 illustrates such modification wherein reference characters 3 3 3 3 3,, represent coils corresponding to secondary windings 3a and 3b associated with the magnetic cores 1a and 1b of FIGURE 1, numerals 2 2 2 2 2,, represent resistors corresponding to the resistor 10 of FIGURE 1, numerals 4 4 4 4 4 represent condensers corresponding to the condenser 6 of FIGURE 1, K K K K K represent switches corresponding to the switch 13 of FIGURE 1 for controlling signal while O O O O represent output terminals corresponding to the output terminal of FIGURE 1, it being understood that each of thesse units is corresponding to the respective key of each keyboard. Single variable resistor 14 of FIGURE 2 corresponds to the resistors 8 and 9 for controlling attenuation time as Well as switches 11 and 12 of FIGURE 1.

While FIGURE 2 differs from FIGURE 1 in that adjustment of length of the attenuation time is not effected 4- stepwisely but continuously because a variable resistor is used for the control of the attenuation time, it will be clear to those skilled in the art that stepwise change-over switch may be used, if desired.

While the invention has been explained by describing particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claim.

What I claim:

An attenuating sound control system for electronic musical instruments to regulate the attenuation time at the termination of a sound, comprising, in combination;

a pair of magnetic cores, each having primary and secondary winding, said primary windings and said secondary windings each being connected in series;

D.-C. bias means to bias said primary windings;

a primary oscillation circuit including said serially connected primary windings;

a secondary oscillation circuit including said serially connected secondary windings, said secondary oscillation circuit having a tuning frequency of l/n of the tuning frequency of said primary oscillation circuit, Where n is an integer;

at least one resistor connected in series with said secondary oscillation circuit; and, switch means for short circuiting said resistor and for adjusting said resistor so as to control the attenuation time of the oscillation in said circuit at the time of stopping said oscillation.

References Cited by the Examiner UNITED STATES PATENTS 2,117,752 5/38 Wrathall 321-69. 2,146,053 2/39 Campbell 321-69 2,403,090 7/47 Larsen 84-1.19 2,462,322 2/49 Huge 321-69 2,463,540 3/49 Huge 321-69 2,827,570 3/58 Lynn 321-69 2,875,398 2/59 Stateman 321-69 2,948,818 8/60 Goto 331- X 2,948,819 8/60 Goto 331-165 X DAVID J. GALVIN, Primary Examiner.

CARL W. ROBINSON, GEORGE N. WESTBY,

Examiners. 

